1. Field of the Invention
The present invention relates to a field emission device using resistors and a method for fabricating the same.
2. Description of the Related Art
FIG. 1 is a sectional view of a field emission device using resistors. FIG. 2 is a perspective view of a field emission device using resistors. As shown in FIGS. 1 and 2, in a conventional field emission device using resistors, a plurality of cathodes 2 are formed on a rear substrate 1. Resistor layers 3 are formed on the cathodes 2. A plurality of microtips 2' are formed on the resistors 3 in an array pattern. The microtips 2' are formed in holes 4a of an insulating layer 4 formed on the cathodes 2. Gates 5 having openings 5a corresponding to the holes 4a are stacked on the insulating layer 4. Here, amorphous silicon or a heat-resistant cermet such as Cr--SiO.sub.2 is generally used as a material of the resistor layer 3.
FIG. 3 is a sectional view of a field emission device using general resistors, having another structure. FIG. 4 is a perspective view of a field emission device using general resistors having a structure different from the structure of the field emission device of FIG. 1. The field emission device shown in FIGS. 3 and 4 is different from the device shown in FIGS. 1 and 2 in that resistors 13 are not entirely stacked on cathodes 12 but partially stacked on the cathodes 12 arranged in holes 14a of an insulating layer 14 and that microtips 12' are formed on the local resistors 13. A substrate 11, the cathodes 12, the insulating layer 14, and gates 15 shown in FIGS. 3 and 4 are slightly different from those of FIGS. 1 and 2.
As shown in a stabilized gate voltage (Vg)-current (I) characteristic curve such as the curve (B) of FIG. 5, the above-mentioned field emission devices using general resistors can be protected from excessive current, thus having a longer life in an wide operation area in which an electron emission (a flow of current) is generated. Namely, according to a gate voltage-current characteristic of a general field emission device in which resistors are not used, electron emission rapidly increases as a gate voltage increases as shown in the curve A. However, in the case of the field emission device using resistors, the electron emission is slow according to the increase of the gate voltage. Accordingly, a slow gate voltage-current characteristic curve such as the curve B is obtained.
However, the field emission device using the amorphous silicon or the heat-resistant cermet such as Cr--SiO.sub.2 as the material of the resistor layers 3 and 13 has the following problems. First, resistor layers 3 and 13 have poor adhesion to the cathodes 2 and 12, thus complicating the fabrication processes.
Second, the resistor layers 3 and 13 are easily eroded by HNO.sub.3 base in a process of removing an Al sacrificial layer (not shown) during the formation of the microtips 2' and 12', thus complicating the fabrication processes. Third, a doping level is hard to stabilize in the resistor layers 3 and 13. Accordingly, the reliability and reproducibility of the fabrication process is deteriorated. Fourth, electron-beam deposition and a sputtering method are used for forming Cr--SiO.sub.2 resistor layers. However, the doping level is hard to control and the fabrication process is complicated.